Typically, a motorcycle utilizes a tubular frame that cradles an engine and attaches to a front and a rear suspension. The tubes of the tubular frame may be forged and then welded or fastened together. Depending on the tubular frame structure, the frame may be relatively less rigid thus increasing the propensity of the frame to flex. Increased flexing of the frame may enhance vibration and noise. Moreover, welding and mechanical fastening of the tubular frame members may increase point-to-point dimensional tolerances.
Typically, a plastic and independent air box couples to the engine. The air box filters and directs air into the intake of the engine and is positioned between the tubular frame and the engine. It will be appreciated that one way to increase the structural rigidity of the tubular frame is to enlarge the frame by, for example, increasing the diameter of the tubing. It will also be appreciated that one way to increase airflow through the air box is to increase the volume of the air box. With the above in mind, both the tubular frame and the air box compete for an allocation of space and gross weight on the motorcycle.